Ablation instrument for intracardiac treatments

ABSTRACT

The invention relates to an ablation apparatus for intracardiac treatments which comprises a high-frequency source whose power output is controlled in a power-or temperature-controlled mode. Ablation catheters which each comprise at least one energy-emitting pole can be used with the apparatus, the or each pole comprising at least one temperature sensor for measuring the temperature of a tissue. The temperature sensors of the poles are either thermistors or thermocouples. The instrument further comprises a sensor-detection system and corresponding devices by means of which the power output can be automatically regulated such that the power is regulated according to the actual catheter type. To that end, it is not necessary to use a specially coded catheter and no special manual operations are necessary for adjusting the catheter type.

This application is a 371 of PCT/E97/06525 Nov. 21, 1997.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an ablation apparatus for intracardial hearttreatments with a high-frequency energy source (RF source for short) andto a method for operating the apparatus.

2. Description of the Prior Art

During the ablation, tissue layers in the heart are denatured by meansof a flexible catheter in order to eliminate disturbances of thestimulus conduction system. Disturbances of this kind manifestthemselves as heart arrhythmias (e.g. tachycardia). The disturbingstimulus conductors are localized and then intentionally interruptedusing the ablation catheter. The tissue lesion carried out for theinterruption is performed with the help of high frequency alternatingcurrents of an RF source. The power output of the RF source is adjustedby means of a temperature regulation in such a manner that the cells arenecrotised, but that the cellular composition (the tissue) is notdestroyed and that no coagulation takes place at the pole giving off theenergy.

Ablation apparatuses are composed of an apparatus part which containsthe RF source and at least one catheter which is connected to the RFsource and has one or more poles which give off energy.

Different types of catheters are used, for example those which differ inthe temperature sensors at the poles. These sensors can be thermistorsor thermoelements.

As a result of inhomogeneities in the heat conduction, a temperaturedistribution with different temperatures can arise on the pole. Thetemperature sensor measures an average temperature and thus localoverheatings can arise on the pole. The temperature relationships on thepole can be better measured with a plurality of temperature sensors.

The pole can be assembled from a plurality of separate segments, whichare all connected to the same RF source and each of which contains aseparate temperature sensor. The ablation can also be carried out usingtwo catheters which are separate but connected to the same RF source andact on the same tissue location. In this case the poles of the twocatheters represent two segments of a common pole or else two oppositepoles.

Catheters are also known which have no temperature sensors.

There is also a large variety of catheters which differ with respect todifferent sensor types (when there is a sensor present) and/or whichdiffer with respect to the number of sensors, which can also be zero.

In known ablation apparatuses (e.g. the Cordis-Webster/Stockert “EPshuttle”) the catheter type must be set manually. This manual setting isan action which must be performed specially by the user and which canlead to an error in the operation as a result of a confusion of thecatheters.

U.S. Pat. No. 5,383,874 describes catheters with codings which make thetype of the catheter recognisable by the apparatus. These catheters canhowever be used only with apparatuses which are capable of decipheringthis coding. Conversely, only catheters which contain this coding can beused with these apparatuses.

SUMMARY OF THE INVENTION

The object of the invention is to provide an ablation apparatus whichpermits a free choice from a wide selection of catheter types, whereinoperating errors should be largely avoidable in cases which are possiblein practice.

The ablation apparatus for intracardial heart treatments has an RFsource, the power output of which takes place in a regulated manner in apower or temperature regulated mode. Ablation catheters, each of whichcomprises at least one energy output pole can be used with theapparatus, with it being possible for the or each pole to contain atleast one temperature sensor for the measurement of a tissuetemperature. The temperature sensors of the poles are either thermistorsor thermoelements. A sensor recognition and corresponding means areprovided, as a result of which the regulation for the power output canbe automatically set in such a manner that the carrying out of the powerregulation corresponds to the current catheter type. In this situationit is not necessary for the catheter to have a special coding and nospecial manual acts of the user are required for setting the type ofcatheter.

DETAILED DESCRIPTION OF THE PREFERRED EXEMPLARY EMBODIMENTS

The ablation apparatus has a sensor recognition and corresponding means,as a result of which the measurement values of current sensors areautomatically used for the regulation of the power output. A switchoverto the type of catheter which is connected is automatically and reliablydone through the sensor recognition.

Measurement circuits for the thermistor or the thermoelementrespectively are designed for the automatic recognition as follows: 1.The thermistor measurement circuit can distinguish the states “open”,“short circuit” and “valid sensor”. 2. The thermoelement measurementcircuit can distinguish the states “open” and “not open” as well asadvantageously “plausible temperature value”. (The “short circuit” statecan not be distinguished by the thermoelement measurement circuit sincea thermoelement which has the same temperature as an associatedcomparison location appears as a short circuit.)

A recognition algorithm of the sensor recognition operates asfollows: 1. If the state “open” is detected by the currently activemeasurement circuit the thermistor measurement circuit is alwaysswitched on. 2. If the thermistor measurement circuit detects a “validsensor”, then the result of the automatic recognition is “thermistor”.3. If the thermistor measurement circuit detects a short circuit, theresult of the automatic recognition is “thermoelement”. (The thermistormeasurement circuit then can be deactivated and the thermoelementmeasurement circuit activated.)

The sensor type recognition will be described in somewhat more detail inthe following:

The ablation apparatus contains two measurement circuits for thedetermination of the temperature present at the thermistor orthermoelement respectively. These measurement circuits can be activatedindividually. The automatic recognition can also be carried out usingthem in that resistances between the hook-up connectors of the sensorsare determined. “States” of the sensors can be associated with themeasured resistances:

a) The thermistor measurement circuit can distinguish the states “open”,“short circuit” and “valid sensor”. “Open” is recognized when a certainresistance value is exceeded, i.e. when a temperature derived from themeasurement is correspondingly dropped below. “Short circuit” isrecognised when a certain resistance value is dropped below, i.e. when atemperature derived from the measurement is correspondingly exceeded.“Valid sensor” is recognized when the resistance measured lies betweenthe values beyond which “open” and “short circuit” respectively arerecognized, i.e. when a temperature derived from the measurement lies ina predetermined range.

b) The thermoelement measurement circuit can distinguish the states“open” and “not open” as well as advantageously “plausible temperaturevalue”. The “short circuit” state can not be determined directly by thethermoelement measurement circuit since a thermoelement which has thesame temperature as an associated comparison location appears as a shortcircuit. The “open” state can be recognized through a suitably designedcircuit for example in that “pull-up” or “pull-down” resistancesrespectively “pull” towards a given value which is not accepted by thecircuit which is in operation with a thermoelement connected.

The state “plausible temperature value” is recognised when a temperaturederived from the measurement lies in a predetermined validity range. Inthis situation the sensor operates as follows:

1. If the momentarily active measurement circuit recognized the “open”state, the thermistor measurement circuit is always switched on.

2. If the thermistor measurement circuit recognized the “open” state,then the result of the automatic recognition is “open”. Consequentlyonly power regulation instead of temperature regulation is possible.

3. If the thermistor measurement circuit recognized a “valid sensor”,then the result of the automatic recognition is “thermistor”. Thethermistor measurement circuit thus remains activated and a temperatureregulated ablation is possible.

4. If the thermistor measurement circuit recognized a short circuit,then the result of the automatic recognition is “thermoelement”.Thethermistor measurement circuit is thereupon deactivated and thethermoelement measurement circuit is activated.

5. If the thermoelement measurement circuit recognized a state otherthan “open”, then the temperature regulated ablation is possible.

In addition to the sensor type recognition, means are advantageouslyprovided by means of which one or more tests can be carried out whichare concerned with whether the connected sensors are providing plausibletemperature values: The temperature values should lie in the expectedranges. When catheters with thermoelements are used, it can whereappropriate also be determined using tests whether comparison points ofthe thermoelements are also providing plausible values.

Additional means are advantageous by means of which the measurementcircuit for the temperature measurement can be calibrated and tested.

For the observation of the thermal effect on the tissue arising duringthe ablation, one or several of them can be provided on the tissue as atemperature sensor. It is however also possible that no sensor ispresent or that a sensor is defective.

Thus in the automatic sensor recognition, means are advantageous bymeans of which the number of connected sensors can automatically bedetermined and by means of which the ablation apparatus can be setaccordingly.

Furthermore, means are advantageous with the use of which a monitoringof the start phase can be carried out as a result of the informationfrom the sensor recognition. Through a monitoring of this kind it is tobe prevented that the ablation apparatus inadvertently starts in a powerregulated mode instead of in the temperature regulated mode in the eventthat no sensors are detected. This is a case of an “intelligent start”of the apparatus in accordance with the invention. It is carried out bythe following algorithm, which is associated with the named monitoring.

As soon as a catheter with a temperature sensor is connected and this isrecognized, the monitoring is automatically activated. If now an RFoutput is started with a temperature sensor connected, then thisproceeds without further operating actions, i.e. an RF output is startedin the temperature regulated mode. If, however, a catheter without atemperature sensor was connected in the meantime, or if the temperaturemeasurement circuit is open due to a defective sensor or an intermittentcontact, then a query results as to whether the RF output shouldactually be done in a power regulated mode. If this is negated, then theprocess is interrupted (i.e. the RF output is not started) and themonitoring remains active. If it is affirmed, however, the monitoring isdeactivated. The RF output is now started immediately in the powerregulated mode or it can be started by means of a further push of abutton. From now on, further RF outputs can be started in the powerregulated mode without the start having to be confirmed in each caseuntil a catheter with a temperature sensor is again connected. Themonitoring is advantageously activated after switching on the apparatusso that a catheter with a temperature sensor is always requested at thebeginning.

In the following a few further supplementary explanations are made onthe algorithm concerning the “intelligent start”.

When the measurement circuits report the “open” state, the algorithmdescribed in the following prevents an inadvertent start in the powerregulated mode while simultaneously minimising the operating action.This start blocking comprises the following items:

1. As soon as a catheter with a temperature sensor is connected and thisis recognized, the monitoring is automatically activated. If now an RFoutput is started with a temperature sensor connected, then thisproceeds without further actions on the part of the user, i.e. an RFoutput is started in the temperature regulated mode.

2. If, however, a catheter without a temperature sensor was connected inthe mean time or the temperature measurement circuit is open due to adefective sensor or an intermittent contact, then a query results as towhether the RF output should actually be done in a power regulated mode.If this is negated, then the process is interrupted (i.e. the RF outputis not started) and the monitoring remains active. If it is affirmed,however, the monitoring is deactivated. The RF output is now startedimmediately in the power regulated mode or it can be started by means ofa further push of a button.

3. From now on, further RF outputs can be started in the power regulatedmode without the start having to be confirmed in each case until acatheter with a temperature sensor is again connected.

The monitoring is advantageously activated after switching on theapparatus so that a catheter with a temperature sensor is alwaysrequested at the beginning.

Catheters with a plurality of sensors and, under certain conditions,with a plurality of ablation poles are also known. In this event thesensor recognition system or a plurality of sensor recognition systemscan be used to determine the number of sensors connected and to set theregulation or the mode of operation of the ablation apparatusaccordingly.

For this, measurement circuits for thermistors and/or thermoelements canbe associated with the possible sensor connections. In order to reducethe number of measurement circuits a group of possible sensorconnections can in each case be associated with one measurement circuit,which can be connected sequentially via a multiplexer to the connectionsof a group.

Various algorithms are conceivable for setting the modes of operation:For example the values of all recognized temperature sensors canautomatically be fed to the regulator when an ablation catheter with onepole is connected. If ablation catheters with a plurality of ablationpoles are connected, a logic circuit can automatically associate certainsensors with each pole.

What is claimed is:
 1. An ablation apparatus for intracardial hearttreatments, the apparatus comprising: an RF source, wherein the poweroutput of the RF source is regulated in a power or temperature regulatedmode; at least one ablation catheter that may be connected to the RFsource and that comprises at least one energy output pole, wherein theat least one energy output pole may contain at least one temperaturesensor and the temperature sensors of the poles are one of eitherthermistors or thermoelements; and a sensor recognition systemconfigured such that regulation of power output may be automatically setin such a manner that carrying out of the power regulation correspondsto the type of at least one ablation catheter without the need for thecatheter to have a special coding and further configured such thatspecial manual actions of a user are not required for setting of thetype of at least one ablation catheter; wherein the sensor recognitionsystem comprises a sensor type recognition system through which theremay be determined whether the temperature sensors of the poles arethermistors or thermoelements.
 2. An ablation apparatus in accordancewith claim 1 further comprising means for carrying out at least one testthat is intended to determine whether connected sensors yield plausibletemperature values.
 3. An ablation apparatus in accordance with claim 2wherein the means for carrying out at least one test may providecomparison points that yield plausible temperature values for thethermoelements.
 4. An ablation apparatus in accordance with claim 1further comprising means for calibrating and testing measurementcircuits for the temperature measurements.
 5. An ablation apparatus inaccordance with claim 1 further comprising means for monitoring of astart phase so that the monitoring may prevent an unintentional start ina power regulated mode.
 6. An ablation apparatus in accordance withclaim 1 further comprising means for determination of the number ofconnected sensors and a plurality of measurement circuits, wherein themeasurement circuits are switched via one or more multiplexers toconnections at which connections a thermo-sensor is to be expected, andwherein the ablation apparatus further comprises means for setting themode of operation of the apparatus to the presence of sensors and thenumber of sensors.
 7. An ablation apparatus for intracardial hearttreatments, the apparatus comprising: an RF source, wherein the poweroutput of the RF source is regulated in a power or temperature regulatedmode; at least one ablation catheter that may be connected to the RFsource and that comprises at least one energy output pole, wherein theat least one energy output pole may contain at least one temperaturesensor and the temperature sensors of the poles are one of eitherthermistors or thermoelements; and a sensor recognition systemconfigured such that regulation of power output may be automatically setin such a manner that carrying out of the power regulation correspondsto the type of at least one ablation catheter without the need for thecatheter to have a special coding and further configured such thatspecial manual actions of a user are not required for setting of thetype of at least one ablation catheter; wherein the sensor recognitionsystem comprises means for determining the number of connected sensors.8. An ablation apparatus in accordance with claim 7 further comprisingmeans for carrying out at least one test that is intended to determinewhether connected sensors yield plausible temperature values.
 9. Anablation apparatus in accordance with claim 7 wherein the means forcarrying out at least one test may provide comparison points that yieldplausible temperature values for the thermoelements.
 10. An ablationapparatus in accordance with claim 7 further comprising means forcalibrating and testing measurement circuits for the temperaturemeasurements.
 11. An ablation apparatus in accordance with claim 7further comprising means for monitoring of a start phase so that themonitoring may prevent an unintentional start in a power regulated mode.12. An ablation apparatus in accordance with claim 7 further thecomprising means for determination of the number of connected sensorsand a plurality of measurement circuits, wherein the measurementcircuits are switched via one or more multiplexers to connections atwhich connections a thermo-sensor is to be expected, and wherein theablation apparatus further comprises means for setting the mode ofoperation of the apparatus to the presence of sensors and the number ofsensors.
 13. A method for operation of an ablation apparatus, the methodcomprising providing: an ablation apparatus for intracardial hearttreatments, the apparatus comprising: an RF source, wherein the poweroutput of the RF source is regulated in a power or temperature regulatedmode; and at least one ablation catheter that may be connected to the RFsource and that comprises at least one energy output pole, wherein theat least one energy output pole may contain at least one temperaturesensor and the temperature sensors of the poles are one of eitherthermistors or thermoelements; providing the ablation apparatus with twoactivatable sensor measurement circuits that are respectively associatedwith a thermistor and a thermoelement; supplying data on the presence ofsensors of a connected catheter with the two activatable sensormeasurement circuits; supplying data on the states of the sensors in acase of a presence of a sensor; deciding as a result of the determinedstates, with a recognition algorithm, whether a sensor measurementcircuit is to be activated and, if so, which sensor measurement circuit;and switching on the power or temperature regulated mode accordingly.14. A method in accordance with claim 13, wherein states “open,” “shortcircuit” and “valid sensor” are distinguished by the thermistormeasurement circuit and states “open” and “not open” are distinguishedby the thermoelement measurement circuit, wherein the thermistormeasurement circuit is activated when the state “open” is determined,and wherein when the thermistor measurement circuit is already activatedand the state “short circuit” is determined, the thermoelementmeasurement circuit is activated.
 15. The method in accordance withclaim 13 further comprising monitoring of a start phase, wherein data onthe presence of sensors of a connected catheter are supplied by at leastone measurement circuit, wherein a decision is made by a recognitionalgorithm whether the operation is to be in the power or the temperatureregulated mode, and wherein in the power regulated mode the startblocking is not deactivated until after a positive reply to a query. 16.A method in accordance with claim 15 or in the monitoring of the startphase is automatically activated when the ablation apparatus is switchedon or when a catheter is recognized as a catheter with temperaturesensors when being connected.
 17. A method in accordance with claim 13wherein the sensors are automatically associated by a logic circuit withcontrol circuits or the control circuit for the temperature regulation.